1. Field of the Invention
The present invention is concerned with apparatus and methods for treating starch-bearing grains such as corn, barley, wheat, rice and milo to cook and gelatinize the same on a continuous or semi-continuous basis for rendering the cooked grain suitable for enzymatic conversion to sugars. More particularly, it is concerned with such methods and apparatus which involve use of an especially configured extrusion cooker designed to handle grain slurries having considerable excess water, while at the same time establishing conditions of temperature, pressure and mechanical shear within the extruder for adequate cooking and gelatinization of the grain.
2. Description of the Prior Art
The production of alcohol from starch-bearing grains is in principle extremely old and well known. Generally speaking, prior practice involves placing the grain and water in a vat-type cooking vessel, followed by heating under pressure for a period of time to cook and gelatinize the grain. Subsequent to this, the cooked grain is treated with appropriate enzymes to break down the starch material into corresponding sugars. Such sugars can then be fermented by known means to give the desired alcohol.
Although alcohol making procedures of this type are widely followed, it will be appreciated that a significant investment in equipment is required. That is to say, in order to make the process economical, relatively large cooking and/or holding tanks must be employed. Moreover, the process is relatively time-consuming and is energy intensive, because of the large amount of heat needed to adequately cook and gelatinize the grain.
Of course, recent shortages of energy have accentuated the above problems. That is to say, the increasing cost of energy has concomitantly increased the production costs associated with conventional alcohol manufacture, thus raising the ultimate cost of this valuable commodity.
Therefore, there is a real need for an energy conserving, continuous or semi-continuous extrusion method for treating starch-bearing grains to yield gelatinized end products susceptible to relatively quick conversion to sugars. Prior patents describing various grain treatment methods include the following U.S. Pat. Nos. 129,906, 2,277,361, 2,884,327, 3,212,904, 3,248,228, 3,397,067, 3,411,429, 3,778,521, 3,778,522, 3,817,261, 3,778,512, 3,133,818, 3,132,948 and 4,128,051.